1. Field of the Invention
The invention relates to microwave antennas generally and to slotted waveguide arrays more particularly.
2. Description of the Prior Art
In the prior art, the edge-slotted waveguide antenna is well-known. Such an antenna may be used singly as a linear array providing a beam sharpened in a single coordinate, or a number of such linear arrays may be stacked to form a planar array. Planar arrays of that type are shown and described in the Patent and Technical Literature. For example, in the text "Radar Handbook" by Merrill I. Skolnik (McGraw-Hill, 1979 (, planar arrays are illustrated in Chapter 13 thereof, especially in FIGURE 15, 27, 29 and 30 in that chapter.
A dual-slot version of the slotted-waveguide antenna is described in U.S. Pat. No. 3,740,751 entitled "Wideband Dual-Slot Waveguide Array" assigned to the assignee of the present application. As this description proceeds, it will be seen that the present invention is adaptable to either the single or dual-slot version.
Still further, U.S. Patent application, Ser. No. 942,070, filed Sept. 13, 1978, entitled "Lightweight Composite Slotted-Wageguide Antenna and Method of Manufacture" assigned to the assignee of the present application describes a type of composite "built-up" plastic material structure in which the slots of an array are covered by a relatively heavy electrically transparent material which acts as a radome for environmental protection of the interior of the waveguide and also as a structural material. The manner in which the present invention can ideally be applied in a planar array constructed according to U.S. Pat. No. 3,740,751, or the aforementioned patent application, Ser. No. 942,070, will be appreciated as this description proceeds.
The concept of constructing an array from which a narrow beam can be produced from a "front" plane and alternatively from a "rear" plane or aperture is not new in the broadest sense. One example is the apparatus described in U.S. Pat. No. 4,044,360 entitled "Two-Mode RF Phase Shifter" "Particularly for Phase Scanner Array." In that patent, a planar array has front and back apertures and if illuminated from the rear aperture can act as a scanable lens comprising a plurality of phase programmed individual elements in the planar array configuration. Alternatively, that device can be operated in a reflective mode in which the array reflects the primary feed energy, (such as a "dish" reflector would do), likewise in a programmable phase pattern for scanning purposes.
The present invention provides a relatively low-cost arrangement for alternative front and rear aperture operation. The manner in which the state of the prior art is advanced by the invention will be understood as this description proceeds.
The recognized problem of maximizing scanning coverage in many radar applications will be seen to be relieved substantially when the system of the invention is employed.